Energy dependence of inclusive photon elliptic flow in heavy-ion collision models

TL;DR

This study compares photon elliptic flow measurements from heavy-ion collisions at RHIC and SPS with AMPT and UrQMD model calculations, revealing energy-dependent effects and the importance of partonic interactions.

Contribution

It provides the first detailed comparison of photon v_{2} at forward rapidities with transport models across a wide energy range, highlighting the role of partonic effects.

Findings

AMPT model agrees well with measurements at RHIC forward rapidities.

Partonic effects are less significant at SPS energies.

Photon v_{2} scales with parent c0^{0} v_{2} with a 44% difference in p_T integrated v_{2}.

Abstract

We present a comparison of inclusive photon elliptic flow parameter (v_{2}) measured at RHIC and SPS high energy heavy-ion collision experiments to calculations done using the AMPT and UrQMD models. The new results discussed includes the comparison of the model calculations of photon v_{2} to corresponding measurements at the forward rapidities. We observe that the AMPT model which includes partonic interactions and quark coalescence as a mechanism of hadronization is in good agreement with the measurements even at forward rapidities (2.3 < \eta < 3.9) at RHIC as was previously observed for measurements at midrapidity. At the top SPS energy the contribution from partonic effects are smaller than that at RHIC energy, based on the comparison of the measured photon v_{2} with those from the AMPT default and UrQMD model calculations. We find that if the measurements in RHIC beam energy scan (BES) and LHC energies would require an energy dependent partonic cross section in the AMPT models, then the observed longitudinal scaling of v_{2} at top RHIC energies (19.6-200 GeV) will be violated. We also discuss the relation between the inclusive photon v_{2} and those of their parent \pi^{0}'s for the beam energies of 7.7 GeV to 2.76 TeV. The model results show that the transverse momentum (p_{\mathrm T}) integrated v_{2} of \pi^{0} is larger by about 44% relative to those of the inclusive photons. Finally we present the expectations of inclusive photon v_{2} for the RHIC beam energy scan (BES) program and LHC from the transport models, so that they can be compared to corresponding measurements using the data already collected at RHIC and LHC.